CT Abdomen - Read Like A Radiologist

Pathology recognition

In the previous sections, you practiced recognizing normal anatomy and systematically assessing a CT abdomen. In this section, you apply that knowledge to pathology. Below are a few general tips for assessing a CT abdomen, followed by two cases. The cases are deliberately kept short. Important — the aim is not to make a definitive diagnosis but to practice recognizing abnormalities on CT and reasoning about what you see.

General tips for recognizing pathology:

1. Look for fat stranding — increased density in normally hypodense mesenteric or peritoneal fat is often a sign of a local pathological process, such as inflammation. Carefully examine the area of fat stranding to determine the underlying cause.
2. Look for asymmetry — the body is largely symmetrical, so compare the left and right sides. Compare both the organs and the surrounding structures. Asymmetry is a red flag.
3. Look for free fluid or free air — both are often pathological and warrant explanation. Free air in the abdomen may indicate perforation of a hollow organ (e.g., a gastric perforation) and is a very important finding. Additional tip: Free air is often best seen on lung window settings.
4. Assess the organ contour — an irregular, nodular, or interrupted contour can indicate pathology, even if a focal lesion is not visible. Examine the region thoroughly and try to correlate it with any other abnormalities. 
5. Pay attention to abnormal densities — a structure that deviates from the expected HU value warrants attention. A density that is too high or too low in an organ or vessel may indicate a pathological process. Also examine the structure in the other contrast phase if a multiphase CT scan was performed.
6. Follow tubular structures — bile ducts, ureters, and bowel wall. Dilation, wall thickening, caliber change, or abrupt interruption may indicate obstruction and/or a local pathological process (e.g., hydronephrosis/hydroureter due to an obstructing ureteral stone).

Case 1. 

Clinical information
Man, 62 years old. Increasing right lower abdominal pain since yesterday, with mild fever (38.2°C) and nausea. Laboratory tests show a slightly elevated CRP and leukocytosis. 
Question 5a
The treating physician requests an abdominal CT. Which phase(s) would you select for this clinical question, and why?

First, look at the CT images, then answer the two questions.

Question 5b
Describe what you see on the CT. Which structure draws your attention, and what do you notice about its immediate surroundings? 

Question 5c
Review the images carefully and in their entirety. In addition to the findings from question 2, do you see any other abnormalities?

Describe what you see and what this means for your final diagnosis.

Answers: see next page.